Regenerative thermal beds are used to capture and store heat from a first hot stream of fluid and then to transfer the heat to a second cold body of fluid before it is reacted such as by combustion, oxidation, reduction or other chemical process whether reacted in the presence or absence of a catalyst.
Originally gravel was used as the packing for the bed. Ceramic saddles and Raschig rings have been utilized for decades. As the saddles and Raschig rings randomly pack into the heat exchanger shell, they may locally stack in an orientation that will block flow. The flow is non-uniform throughout the bed of material and the pressure drop through a heat exchanger containing saddles, gravel or rings is relatively high, usually about 10 inches of water. Furthermore, the locally blocked areas may trap fluid which can contaminate the flow of second fluid or can be exhausted to the environment.
Recently, the use of monolithic columns of ceramic material for the heat exchanger columns in a regenerative thermal oxidizer system for cleaning combustion gas has been disclosed in U.S. Pat. No. 5,352,115. The monolithic columns have a lower pressure drop and reduce contamination experienced with random packing of saddles or rings.
Monolithic columns carrying a layer of catalyst are also used in catalytic processes to synthesize or convert gaseous streams to other products and in the treatment of exhaust gases from combustion engines or from industrial processes. The ceramic columns are coated with catalyst materials, such as rare earth metals. However, it is expensive to manufacture monolithic columns. Furthermore, monolithic columns are rigid and brittle. After repeated cycles of heating and cooling, the column can develop stress cracks and break or shatter into small pieces. The column becomes inoperative requiring replacement of the monolithic element. This can be quite expensive in the case of columns coated with noble or rare earth metals or metallic compounds containing platinum or palladium, rhodium, etc. Also, the channels in monolithic columns are gas-tight leading to no lateral dispersion of the gas flowing in the channels.